1. Field of the Invention
The present invention generally relates to computer systems and more particularly to an operating system which is more easily adapted to run on computers having different firmware designs.
2. Description of the Prior Art
The basic structure of a conventional computer system 10 is shown in FIG. 1. The heart of computer system 10 is a central processing unit (CPU) or processor 12 which is connected to several peripheral devices, including input/output (I/O) devices 14 (such as a display monitor and keyboard) for the user interface, a permanent memory device 16 (such as a hard disk or floppy diskette) for storing the computer's operating system and user programs, and a temporary memory device 18 (such as random-access memory or RAM) that is used by processor 12 to carry out program instructions. Processor 12 communicates with the peripheral devices by various means, including a bus 20 or a direct channel 22. Computer system 10 may have many additional components which are not shown, such as serial and parallel ports for connection to, e.g., modems or printers. Those skilled in the art will further appreciate that there are other components that might be used in conjunction 20 with those shown in the block diagram of FIG. 1; for example, a display adapter connected to processor 12 might be used to control a video display monitor.
Computer system 10 also includes firmware 24 whose primary purpose is to seek out and load an operating system from one of the peripherals (usually permanent memory device 16) whenever the computer is first turned on. The process of seeking out and loading the operating system is referred to as "booting" the computer. Computer system 10 may be designed to allow firmware 24 to initialize (or re-initialize) an operating system without turning the computer off and back on again (a "soft" boot). Firmware 24 is essentially a series of machine instructions which are typically stored in a read-only storage (ROS) device, such as read-only memory (ROM). As shown in the flow chart of FIG. 2, after power to computer system 10 is turned on (or a soft boot command has been received), processor 12 begins to execute the firmware instructions and seeks out an operating system (26). If an operating system is found, it is loaded (28) into temporary memory 18. Thereafter, the operating system allows other application layers to be added, i.e., user software programs (30). In this manner, a given computer hardware construction can be adapted to run a variety of operating systems and user applications.
The foregoing description generally applies to any type of operating system, including two popular operating systems known as MSDOS and UNIX (MSDOS is a trademark of Microsoft Corp.; UNIX is a trademark of UNIX System Laboratories), but the present invention has particular application to UNIX. UNIX is a multi-user, multi-tasking operating system which is available from a variety of sources with different versions. These include, among others, System V (American Telephone & Telegraph), AIX (International Business Machines), and Mach (NeXT Computers). FIG. 3 illustrates a boot image 32 that is loaded as a UNIX operating system. Boot image 32 includes a base kernel portion 34 and a boot filesystem portion 36. Kernel 34 acts as the intermediary between user programs and hardware devices, and includes, among other things, device drivers. Boot filesystem 36 is the RAM-based file system that provides user commands to manipulate computer objects, such as files, directories, and symbolic links. When firmware 24 sees boot image 32 (such as on a floppy diskette, hard disk, or CD-ROM disk), it transfers control to that operating system (kernel 34) after loading boot filesystem 38.
A given operating system can be adapted to run on various types of hardware platforms. With some operating systems, such as MSDOS, a given copy of the operating system can be used to boot computers manufactured by many sources, since the hardware architecture and BIOS (basic input and output system) functions remain constant from manufacturer to manufacturer. Other operating systems, like UNIX, must be more portable due to significant differences between the various types of hardware that have been designed to run UNIX. In this regard, boot filesystem 36 includes information that is hardware dependent, such as the PAL (Portability Assist Layer or Platform Abstraction Layer), which contains the specific instructions for communicating with the particular hardware devices of a given manufacturer.
One other factor, similar to hardware dependencies, that can make an operating system less portable is its dependency on firmware. Most operating systems have many firmware dependencies. Two specific areas that affect portability of an operating system are hardware initialization and a mechanism for describing the capabilities of the computer system. These functions as performed by a system's firmware vary widely. Operating systems have to be modified to support these differences with changes that can be scattered throughout the software, i.e., for a UNIX-type workstation, the differences are not addressed by the PAL, and so the kernel must be rebuilt, which can be a major issue when it comes to porting an operating system to new hardware. It also can become an issue when a system's hardware/firmware do not work correctly, or when hardware-specific states or functions are left by the firmware which are incompatible with the operating system. For example, the kernel cannot clear a hot interrupt that is left from the firmware. Sometimes the kernel also needs certain information which would normally be passed by control blocks in the firmware, such as the type of processor in the computer system, the bus architecture, the time and date, etc. It would, therefore, be desirable to provide a method to isolate an operating system from firmware dependencies. It would be further advantageous if the method allowed correction or modification of firmware functionality.